Telephone system



Jan. 274, 1939. E, s GIBSON 2,145,079

TELEPHONEISYSTEM Filed Feb. 29, 1936 lOSheets-Sheet l 9 "3 m S s Q s k u. k I I a ik 0,

Q I T INVENTOR Q g 3 ES. GIBSON Q) l: c m ggw A 7' TORWE V Jan. 24, 1939. E. s. GIBSON 2,145,079

TELEPHONE SYSTEM Fiied Feb. 29, 1936 10 Sheets-Sheet 2 POL ARIZ so POLAR/ZED Jan; 24, 1939. E. s. GIBSON TELEPHONE SYSTEM Filed Feb. 29, 1956 l0 Sheets-Sheet 3 Na \a m2 m2 tn 5 ma 2. QM Q E E 2m in Qwowm 3m Sn QR NR mom \\m ma 9 m3 Um UP k2 llln III U Ill Dl -II DI IlIIDDI II DI III DII IIII DII Em 90m 9% QQM fl 1U PIIILU D II IN VENTOR E. S. GIBSON GPM A TTORNE Y Jan. 24, 1939. E. s. GIBSON 2,145,079

' TELEPHONE SYSTEM //v VEN 70/? E S. GIBSON A TTORMEV Jan. 24, 1939 E. s. GIBSON 2,145,079

TELEPHONE SYSTEM Filed Feb. 29, 1956 10 Sheets-Sheet 5 IN [/5 N TOR E s. a/Bso/v A 7' TORNEV Jan. 24, 1939. E. s. GIBSON 2,

TELEPHONE SYSTEM I Filed Feb. 29, 1936 10 Sheets-Sheet 6 Qunmmu llllllllllll llllllllllll FIG. 6

l Nl /EN TOR 5. GIBSON BY Q-M A TTORNE V Jan. 24, 1939. E. s. GIBSON 2,145,079 Y TELEPHONE SYSTEM Filed Feb. 29, 1936 10 sheets-sheet 7 MARG/NAL I /N VE N TOP 5 s. a/eso/ v By 6356M A 7" TORNE) Jan. 24, 1939. E. s, GIBSON TELEPHONE SYSTEM Filed Feb. 29, 1936 10 Sheets-Sheet 8 new wom Rm 2% Run awn 53. mm

o lNVENTO/P 0 ESG/BSON ATTORNEY Jan. 24, 1939.

E. s. GIBSON 2,145,079

TELEPHONE SYSTEM FiLed Feb. 29, 1936 10 SheetsSheet 9 lNl/EN 70/? E S. GIBSON A TTORNEV Jan. 24, 1939.- 0 E. s. GIBSON 2,145,079

TELEPHONE SYSTEM Filed Feb. 29, 19:56 10 Sheets-Sheet 10 nvl E/vrok ES. GIBSON By $6M A 7' TO/PNEV Patented Jan. 24, 1939 UNITED STATES PATENT OFFICE TELEPHONE SYSTEM I Earl S. Gibson, Ridgewood, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York This invention relates to telephone systems and more particularly to systems in which connections are established by automatic selector switches under the control of a sender in which the designations of wanted lines are registered in response to the keying of digits at an operators position;

More specifically the invention relates to a sender for enabling an operator at a toll or A switchboard to control the setting of selector switches to complete desired connections.

It has been heretofore proposed to provide a plurality of senders any one of which may be taken for use by any one of a plurality of operators and to provide each operator with a single set of digit keys by means of which she may.

cause the registration of digits of any desired line designation on the registers of the sender associated with her position.

For the purpose of registering the digits keyed by an operator, the sender is equipped with groups of register relays which in accordance with the digit registrations set up thereon control the operation of impulse transmitting means to transmit series of impulses for setting selector switches. Such a system is disclosed in Patent 1,916,760, granted July 4, 1933 to l. H. Henry.

It is the object of the present invention to provide in senders of the foregoing type a simplified digit registering mechanism and an impulse transmitting mechanism which may be readily and accurately adjusted to transmit impulses at a desired speed and with a desired ratio between make and break periods.

In accordance with the present invention, the sender comprises a digit registering device of the cross-bar type having a capacity for registering all of the digits of any desired line designation, impulse generating and counting means comprising two gaseous conductor tubes, means for enabling the operator to control the crossbar register from a single set of digit keys to successively register the several digits of the line designation keyed by the operator and means for causing the impulse generating and counting means to successively transmit series of impulses in accordance with the digits registered.

The cross-bar register may for example be of the type disclosed in the Patent No. 2,021,329 granted on Nov. 19, 1935 to J. N. Reynolds, and comprises five horizontal bars and as many vertical bars as are necessary to register the maximum number of digits of any line designation or as illustrated eight digits. Two selecting magnets are provided for rotating each horizontal responding to the eight holding magnets; Any

contact set may be operated by the operation of one of the selecting magnets to rotate a horizontal bar toward the horizontal row in which 'a particular contact set is located followed by the operation of a holding magnet to rotate a vertical bar corresponding to the vertical row in which the contact set is located. Each vertical row of ten sets of contact springs serves as a register for registering one of the digits of any subscribers line designation.

To register the several digits of a subscribers line designation, keys of an operators set corresponding'to the numerical values of the digit are successively operated. Each operation of a key causes the operation of that one of the selecting magnets which has the same numerical value. Associated with each holding magnet is a transfer relay, the holding magnets and associated transfer relays serving as a steering switch to enable successively keyed digits of a line designation to be successively registered on contact sets of successive vertical rows. Thus in response to the depression of a key for the first digit, one of the ten selecting magnets is operated followed by the operation and locking of the first holding magnet, then followed by the release of theoperated selecting 'magnet when the key is released. During the time that the selecting and holding magnets are both operated, one of the ten contact sets of the first vertical row corresponding to the numerical value of the first digit keyed is operated and held operated by the first holding magnet after the selecting magnet releases. The release of the selecting magnet permits the transfer relay associated with the operated holding magnet to operate in the locking circuit of the magnet preparing the register for registering the next digit to be keyed. In response to the keying of the second digit one of the ten selecting magnets is again operated followed by the operation andlocking of the second holding magnet and the release of the operated selecting magnet, thus operating a contact set of the second vertical row corresponding to the numerical value of the second digit. This contact set is held operated by the second holding magnet after the selecting magnet releases and the transfer relay associated with the second holding magnet is operated to prepare the register for registering the next digit. In a similar manner the several digits are registered.

The invention has been illustrated herein as applicable to a system in which an idle one of a plurality of identical senders is associable with any one of a plurality of operators positions by means of a link circuit. The link circuit has access to all of the senders and to all trunks outgoing from the operators position and thus when any operator plugs a cord circuit of his position into the jack of an outgoing trunk, an idle link circuit is started to select the seized trunk and to connect it with an idle sender thereby establishing circuits from that operators position to the sender and from the sender to the selector switch in which the trunk terminates. Such a system is disclosed in the patent to Henry hereinbefore referred to. Since in accordance with the present invention it is necessary to provide eleven operating leads from the key-set of the operators position to the selecting magnets of the register of the sender which is connected to the operators position, the setting of the sender register cannot be controlled over the circuits extending through the link circuit, trunk and cord circuit and therefore an auxiliary key-set connector is provided. This connector is also a cross-bar switch of the same general character as the cross-bar register. The five horizontal bars of the key-set connector are operable by ten selecting magnets which are controllable from the key-set circuits of ten operators positions and the ten vertical bars are operable by ten holding magnets. One hundred sets of contact springs are provided arranged coordinately in ten vertical rows of ten sets each, each horizontal row of contact sets being allocated to one of the ten operators positions and the vertical rows of contact sets being allocated in pairs to five senders. Thus by the operation of the selecting magnet allocated to any one of the ten operators positions followed by the operation of the two holding magnets allocated to any one of five senders, two contact sets are operated whereby eleven operating leads may be extended from the key-set circuit of that operators position to the register sender. It is thus possible to operatively associate the key-set of any one of ten operators positions with the cross-bar register of any one of five senders. For determining which one of the five senders shall be connected with an operators position, an allotter is associated with the connector and with all five senders, the allotter functioning upon the association of a sender with an operators position over the link circuit to allot the holding magnets allocated to that sender for operation in response to the operation of the selecting magnet allocated to that operators position.

In accordance with a further feature of the invention, an impulser having gaseous discharge tubes is provided for transmitting impulses in accordance with the digits registered on the sender register. The impulser comprises two gaseous discharge tubes of the cold cathode type, one tube controlling the operationand release of a pulsing relay which opens and closes the impulsing loop extending to a selector switch while the other tube operates a counting relay to control a counting circuit to count the impulses transmitted. The control cathode of each tube is connected through adjustable resistances to the positive terminal of a source of current and through a condenser to the anode of the other tube. The anode of the first tube is connected through the winding of the pulsing relay and a resistance to the positive terminal of the source of current. The anode of the second tube is connected through the winding of the pulse counting relay and a resistance to the positive terminal of the source of current and the anodes of both tubes are connected together by a third condenser. The second cathode of each tube is arranged to be connected to the grounded or negative terminal of the source of current when it is desired to start the tubes. For example, to start the impulser ground is first connected to the second cathode of the first tube followed almost immediately by the connection of ground to the the preceding cycle of operations is repeated,'the

two tubes ionizing alternately at a rate which is determined by the condenser timing circuits.

The impulse counting relay of the impulser controls the operation of successive relays of a counting relay train, the number of relays operated during the transmission of each series of impulses being determined by the operated contact set in the vertical row of the register which is at the time associated therewith. For successively controlling the counting and transmission of the successive digits of a registered line designation,

the vertical rows of contact sets of the register are successively associated with the train of counting relays by a group of transfer relays serving as an outpulsing steering switch.

For a more complete understanding of the in vention reference may be had to the following detailed description taken in connection with the attached drawings in which:

Fig. 1 shows an operators cord circuit for ex-. tending connections to dial switching oifices and a portion of the equipment of an operators position;

Fig. 2 shows the operators key-set and the remaining equipment of her position;

Fig. 3 shows a trunk circuit of one group or class terminating in a jack accessible to the operators cord circuit of l, and in a first selector switch and the diagrammatic representation of other selector switches and a called sub-.

scribers line;

Figs. 3B, 3C and 31) show modified strapping necessary when the trunk circuit belongs to other groups or classes;

Figs. 4 and 5 taken together show a link circuit for associating a sender such as is disclosed in Figs. 7 to 10, inclusive, with the trunk circuit of Fig. 3. In Fig. 4 the trunk finder and in Fig. 5 the sender-finder of the link are disclosed;

Fig. 6 shows a key-set connector for associating the key-set of any one of a plurality of operators' positions such as is shown in Fig. 2 with any one of a plurality of senders such as is disclosed in Figs. '7 to 10, inclusive;

Figs. '7 to 10, inclusive, show a sender circuit; Fig. 7 showing control relay equipment; Fig. 8 disclosing further control relays and the impulse counting relays; Fig. 9 showing the registering equipment; and Fig. 10 showing further control relays and the impulsing apparatus; and

Fig. 11 is a diagram showing the manner in which the several figures of the drawings should be assembled to disclose the complete embodiment of the invention.

The trunk finder 450 shown in Fig. 4 may be of the well-known Strowger type having both rotary and vertical stepping movements but, being used as a hunting switch, is also equipped with a vertical commutator and commutator brush. In addition, it is equipped with additional brushes to afford other points of access to control conductors extending to trunk circuits.

The sender-finder 550 of Fig. 5 is of the wellknown step-by-step rotary type having no definite normal position and always remains standing when idle on the terminals of the sender last used in extending a connection.

The selector switches disclosed diagrammatically in Fig. 3 may be of the well-known Strowger type responsive to directive impulses transmitted thereto from the sender. As heretofore stated the register equipment of the sender shown in Fig. 9 and the key-set connector disclosed in Fig;

Answering a call from an incoming trunk It will first be assumed that a call is incoming to the operators position of Fig. 1 over the trunk jack IOI and that the operator answers the call by inserting plug I00 of her cord circuit into jack IOI. She then depresses her cord key I02 to the right or talking position. A circuit is thereupon established from battery through the lower winding of relay I03, the uppermost right contacts of key I02, conductor I04 to ground at the normal contacts of relay I05. Relay I03 upon energizing closes at its lower contact a circuit extending from ground at contact I06 of key I02, over the lower contact of relay I03, in parallel to battery through the windings of relays I535 and I01. These relays thereupon operate, relay I05 removing ground from conductor I04 to prevent another cord relay such as relay I03 from operating and connecting ground to conductor I08, whereupon a circuit is established through the upper inner contacts and upper winding of relay I03 to battery to hold relay I03 locked so that as long as key I02 is in its operated position, relay !03 individual to the cord circuit and relay I05 common to the cord circuits of the operators position are held operated. Relay I03 splits the cord circuit and associates the group of conductors I09 with the cord circuit.

The operation of relay I01 connects the tip and ring talking conductors H0 and III of the operators headset circuit, over conductors H2 and I I3 extending to the left or monitoring contacts of key I02 and opens conductor I33. If at this time the key I02 of another cord circuit of the position is operated to the left or monitoring position, the operator will be able to talk or listen on both cord circuits but will beable to split, transfer or key pulse on only the cord circuit, the listening key I02 of which has been operated to the right or talking position. The functions of the splitting key II4, talking and monitoring key I02, and ringing key IIE for enabling the operator to talk, monitor or ring on either end of the cord circuit are fully described in Patent 1,675,956, granted July 3, 1928 to L. F. Porter and will not therefore be discussed in detail herein.

Upon the operation of key I02 a circuit is also established from high resistance ground on the sleeve of jack IOI, over the sleeve of plug I00, contact H6 of key I02 to battery through the windings of relays II! and H8. Relay H8, upon operating, closes an obvious circuit for relay H0. Relay I I1 being marginal does not operate at this time. At its inner upper contact relay II9 connects ground through high resistance I to conductor I2 I to prevent a false operation of the rear cord supervisory lamp I22 should the operator depress a talking key of another cord of her position to the talking position, either accidentally or otherwise, with such cord circuit normal. At its upper back contact relay II9 disconnects the busy test conductor I23 of the operators headset from the tip of answering plug I00 and at its outermost upper and lower front cont-acts establishes a talking circuit which may be traced from conductor -lI0 over the uppermost front contact of relay II 0, the upper normal contacts of splitting key II4, conductor 200, the uppermost normal contact of relay 20I, conductor 202, the uppermost alternate contacts of relay I03, the upper right normal contacts of key H5, over the tip contacts of plug I00 and jack IOI, thence over the toll trunk returning over the ring contacts of jack IOI of plug I00, the inner lower alternate contacts of relay I03, conductor 203, the lower back contact of relay 20I, conductor 204, the right lower normal contacts of key M4, the lower front contact of relay III! to conductor III. -The operator is now enabled to receive instructions over the toll trunk for the further extension of the connection.

'Having received instructions and it having been assumed that a connection is desired with the subscribers line 300, the operator proceeds to test the trunks extending to the ofiice in which the line 300 terminates by touching the tip of the plug I24 to the sleeves of the trunks. A circuit is thereupon established from the tip of plug I24 over the inner lower left normal contact of key N5, the uppermost front contact of relay I03, conductor 205, the upper back contact of relay 206, conductor 201, the upper left normal contact of key II4, the upper back contact of relay I25, to the test lead I23. It will be assumed that the trunk terminating in jack I tests idle andthat the operator on receiving no busy click in her headset, inserts the plug I24 into jack 30f. A circuit is thereupon established from ground through the lower high resistance winding of the trunk sleeve relay 302 over the sleeves of jack 3M and plug I24, contacts I23 of key I02 to battery through the windings oi relays I21 and I28. Due to the high resistance of relay 302, marginal relay I21 does not operate at this time, but relays I28 and 302 both operate' With. relay I28 operated, an obvious circuit is established for relay I25 which there upon operates, opening the connection between the tip of plug I24 and the test conductor I23 and establishing a talking path from the tip and ring conductors H0 and III of the operators headset circuit to the'left normal contacts of splitting key H4, thence over normal contacts,

upper front contact, relay of relay 206, alternate contacts of relay I03, to the tip and ring contacts of plug I24. At its I25 also connects ground through high resistance I29, to conductor I30 for preventing the false operation of the front supervisory lamp I3I should the operator depress a talking key of another cord of her position to the talking position either accidentally or otherwise with such cord circuit normal.

Starting a link circuit to hunt for the selected trunk Relay 302 of the trunk circuit upon operating establishes an obvious circuit for relay 303 which in turn establishes a start circuit for starting an idle link in search of the trunk which has been taken for use and in search of an idle sender. This start circuit may be common, for example, to a group of ten trunks and extends from ground at the lower back contact of relay 304, lower front contact of relay 303, conductor 305, through the Winding of group relay 400 of the link circuit which has first choice access to the group of trunks in which the selected trunk is located. Relay 400 upon energizing connects ground over its upper contact to segment 401 of the group commutator of the trunk finder 450, corresponding to the bank level in which the selected trunk appears, in the case assumed, the first or lowermost segment, and establishes a circuit from ground at the back contact of relay 40I over the lower contacts of relay 400, the lower normal contacts of make busy jack 402, conductor 403., the lowermost back contact of relay 500 to battery through the winding of relay 50I. Relay 50I energizes in this circuit and establishes a circuit for relay 502 extending from ground over the lower front contact of relay 50I, inner lower back contact of relay 503, conductor 504, back contacts of vertical magnet 404 and rotary magnet 405, conductor 505, to battery through the upper winding of relay 502.

With relay 502 operated a circuit is now established for the vertical magnet 404 of the trunk finder 450 which may be traced from battery through the winding of magnet 404, conductor 506, the lower back contact of relay 501, contact of relay 502, to ground at the inner upper back contact of relay 500. Magnet 404 upon operating opens at its back contact the circuit of relay 502, whereupon relay 502 in turn deenergizes opening the circuit of magnet 404. Thus magnet 404 and relay 502 reciprocally control each other to cause magnet 404 to step the brushes of finder 450 vertically step by step, until the commutator brush 406 engages the grounded segment 401. When this occurs a circuit is established for relay 501 extending from ground on segment 401, brush 406, conductor 408, the uppermost back contact of relay 500, the upper winding of relay 501, conductor 508, the back contact of rotary magnet 405, conductor 505, to battery through the upper winding of relay 502. Relays 502 and 501 operate in this circuit, relay 501 looking over its lower winding and inner lower front contact, inner lower back contact of relay 500, conductor 509 to ground at the lower alternate contacts of vertical off-normal springs 409, which closed when the trunk finder 450 took the first step off normal. Relay 501 at its lower back contact also opens the operating circuit of the vertical magnet 404.

With both relays 502 and 501 energized, a cirat the lower front contact of relay 50I.

cuit is now established for the rotary magnet 405 extending from battery through the winding of magnet 405, conductor I0, the lowermost front contact of relay 501, the contacts of relay 502 to ground at the innermost upper back contact of relay 500. Magnet 405 upon energizing opens at its back contact the previously traced circuit extending through the upper winding of relay 502 whereupon relay 502 deenergizes, in turn opening the circuit of magnet 405. Thus magnet 405 and relay 502 reciprocally control each other to cause magnet 405 to step the brushes of the finder 450 over the terminals of the first bank level to which they were previously raised until the set of terminals is reached in the level to which the selected trunk is connected. Thereupon a circuit is established from battery through the winding of trunk relay 306, upper front contact of relay 303, upper back con.- tact of relay 304, conductor 301, bank terminal 410, brush 4! I, conductor 4I2, upper front contact of relay 50L winding of relay 5 to ground through the lower winding of relay 502. Relays 305, 502 and 5H operate in this circuit, relay 5H closing an obvious circuit for relay 503 and a locking circuit for relay 50I extending from battery through the winding and inner lower front contact of relay 50I, the lower contacts of relay 5II to ground at the intermediate lower normal contacts of relay 5I2 for holding relay 50I operated after relay 500 operates as later described. Relay 503 upon operating closes at its innermost upper contact a shunt around the lower winding of relay 502 causing the release of relay 502, closes at its lower front contact an obvious operating circuit through the upper winding of relay 500 and at its lower intermediate contact prepares a circuit for relay 5I2. Relay 500 upon operating looks from off-normal ground on conductor 509 over its innermost lower front contact and lower winding, conductor 5I3 to battery at the back contact of relay 4I3 and at its upper and innermost lower back contacts opens the initial operating and locking circuits of relay 501. Relay 501 thereupon releases.

At the trunk circuit relay 306 upon operating establishes an operating circuit for relay 304 which extends from battery through the winding of relay 304, inner upper front contact of relay 306 to ground at the inner upper front contact of relay 303. Relay 304 operates and. locks over its lower front contact to ground at the inner upper front contact of relay 303, removes ground at its lower back contact from start conductor 305, at its upper back contact opens the initial operating circuit of relay 306 and at its upper front contact prepares the operating circuit of relay 308. Following the operation of relay 304, relay 305 is held operated over a circuit extending from battery through its winding, the upper front contact of relay 303, the upper front contact of relay 306, thence over conductor 301 to ground as previously traced. When ground is removed from start conductor 305, group relay 400 releases if there is at the time no other trunk in the same group in a selective condition.

Hunting for an idle sender At the time relay 50I operated immediately following the starting of the link circuit, a circuit was also established for relay 5I4 extending from battery through the win-ding of relay 5I4 over the lower back contact of said relay 5 I 5 to ground At its upper front contact relay 514 establishes a saturating circuit for the test relay 515 which may be traced from battery through the lower winding of relay 515, front contact of relay 514, through the middle winding of relay 515 to ground at the lower front contact of relay 501. Relay 515 does not, however, become energized sufficiently to operate its contacts. At its lower contact relay 514 establishes a circuit for stepping relay 51B of the sender-finder 550 which extends from battery through the winding of relay 516, back contact of stepping magnet 511, lower contact of relay 514 to ground at the upper back contact of test relay 515. Relay 516 upon energizing connects the winding of the stepping magnet 511 to ground at the back contact of relay 515, whereupon magnet 51! energizes, opening the circuit of stepping relay 516. Magnet 51! and relay 516 thus reciprocally control each other thereby advancing the brushes of the sender finder 550 step by step in search of an idle sender. As soon as a terminal set is reached to which an idle sender is connected, a circuit becomes established for test relay 515 extending from groimd through the middle winding of test relay 515, the upper front contact of relay 514, the lowermost back contact of relay 512, the upper winding of relay 515, innermost upper front contact of relay 501, brush 518, conductor inner right back contact of relay 100, inner left back contact of relay 101 to battery through resistance 102, itbeing assumed that the sender of Figs. '7 to 10, inclusive, is at the time idle. Relay 5 I 5 now receiving current through all of its windings operates quickly, locking in a circuit extending from ground over its upper front contact and upper winding, thence as traced to battery at the back contact of relay 101, opening at its upper back contact the operating circuits of relay 516 and magnet 511 and opening at its lower back contact, the operatingcircuit of relay After an interval as measured by its slow releasing characteristics, relay 514 deenergizes and if at this time the trunk finder has completed its operation and relay 503 has operated, a circuit is established for relay 512 extending from battery through the Winding of relay 512, the lower intermediate front contact of relay 503, the lower intermediate back contact of relay 512, the upper back contact of relay 514, the lower front contact of relay 515, to ground at'the lower frontcontact of relay 501. Relay 512 upon energizing closes a holding circuit for itself before it opens its operating circuit, extending from battery through its winding, its innermost lower front contact to ground at the upper front contact of relay 503, opens at its intermediate lower back contact its own initial operating circuit, transfers the looking circuit of relay 501 from ground at the intermediate normal contacts of relay 512 to ground over the upper back contact of relay 514, the lower font contact of relay 515, and the lower front contact of relay 501, connects brushes 414 to 45! inclusive of finder 450 to brushes 520 to 523 inclusive of the sender-finder 550, establishes a circuit extending in parallel through the windings of relay 524 and 525 over its upper front contact, brush 525, conductor 521, through the left and intermediate windings of relay 103, conductor 154, the right normal contacts of relay 850, V

conductor 155, to groundrat the outer right back contact of relay 106 and at its next to upper contact connects battery through high resistance 553, the back contact of relay 524, conductor 534,

brush 423, conductor 424 through the upper winding of relay 302 to the sleeve of jack 301 for the purpose of marking the trunk busy so long as the link circuit is engaged therewith. Relays 525 and 103 operate in the circuit traced but relay 524 being marginal does not operate. At its upper contact relay 525 bridges the upper contacts of relay 501 in the holding circuit of relays 511 and 356 to hold the latter relays operated following the release of relay 501 and at its lower contact establishes an obvious circuit for relay 536 which closes an alternative holding circuit for relay 512 for holding relay 512 operated-following the release of relay 503. I

At the sender upon the operation of relay 103, an obvious circuit is closed for relay 101 which in turn closes an obvious circuit for relay 100. Relay 1013 disconnects battery through resistance 102 to make the sender busy to other senderfinders, connects ground over its outer left front contact to the start lead 108 extending to the sender time alarm circuit and connects the left winding of the sender time alarm relay 109 to conductor H0 and over its right front contact prepares a circuit for relay H 1. Relay 101 at its middle right and inner left front contacts, connects ground to conductors 113 and 114 for providing locking ground for control relays of the sender and at its outer right contact establishes a circuit over conductor 112 through the winding of relay 801 to battery. Relay 801 operates to perform functions later described.

With ground connected to conductor H4 a circuit is now established for controlling the allotter circuit shown in the lower portion of Fig. 6. This allotter circuit comprises a pair of relays individual to each sender, in the case assumed five pairs of relays individual respectively to live senders, relays 580 and 651 being individual to the sender disclosed, relays 600' and 601 to the second sender and relays 605 and 600 the last or fifthsender, the relays individual to the other two intermediate senders not being disclosed. Relay 692 of the allotter circuit is common to all of the five senders. Since it has been assumed that the sender disclosed was idle at the time of its seizure, when ground is connected to the initial operating circuit of relay 501 and the operating circuits of other relays 601 etc. and

connecting ground over its front contact, the lower front contact of relay 601, conductor 115, right back .contact of relay 105, thence in parallel through the right winding of relay 1 11, high re sistance 113, to l8-volt battery and through the left winding of relay 111, condenser 120, high resistance 121 to 48-volt battery. If the operator has not at this time prepared her key-set circuit for key pulsing, relay 11'1 does not operate since the charging current flowing through the left winding of relay 11'! and condenser 720 produces a flux in opposition to the flux produced by'the right winding of relay '11! and cannot operate by the energization of its right Winding alone.

Since the connection to be established is one requiring key pulsing control over the plug I24 of the cord circuit, the operator will operate her pulsing key 209 to the lower position and since it will be recalled that relay I25 has operated, a circuit is now established from battery resistance 245, through the winding of relay 2 I0, inner lower right contacts of key 209, conductor 2, lower contact of relay I25, conductor 2I2, upper normal contacts of relay US to ground. Relay 2I0 operates, looking over its inner upper front contacts to ground at release key 2 I 4 or to ground on conductor 2II, closing at its lower front contact the circuit of the front key pulsing lamp 2I5, removing ground from conductor 2I0 at its upper normal contacts to prevent the operation of relay 2I3 should the key 209 be operated to its upper position in error, and closing at its upper alternate contacts, an obvious circuit for relay 206. Relay 205 upon operating transfers the tip and ring conductors 205 and 208 extending from the tip and ring contacts of plug I24 from the operators headset to the key-set circuit, at its inner upper front contact connects holding ground over conductor 2I1 to the windings of relays I5 and I01 to hold these relays operated so long as the key-set circuit remains associated with the cord circuit, and at its inner lower front contact supplies ground to the inner active contacts of the keys of key-set 220.

Registering the class indication The trunks to which the sender has access are arranged in groups in accordance with the number of digits required to complete a call and further subdivision in grouping may be made as follows: trunks requiring immediate ringing from the sender and trunks not requiring such immediate ringing; trunks requiring 0.6 second timing between the successive transmission of series of impulses and trunks requiring 0.4 second timing between the transmission of series of impulses. Each group may consist of trunks for which the sender is required to pulse out several different numbers of digits under the control of the operators start key 243. The sender determines the class of the call at the time of its seizure by the polarity encountered on conductors 3M, 3I6, M8 and 320 of the trunk to which it is connected.

The sender is arranged to function with four classes of trunks, the class relays I 000 to I003, inclusive, being provided to register these classes. Any class may require a fixed number of digits to be keyed or a variable number of digits, automatic start of ringing or no ringing; 0.6 second or 0.4 second timing between any two series of impulses transmitted to set selector switches. The polarity connected to conductors 3I4, 3I6, 3I8 and 320 extending from each trunk to the sender through the link circuit is determined by the arrangement of straps 309 to 3I2, inclusive.

With the sender now associated with the trunk circuit, the following relays of the sender may or may not be operated dependent on the strapping in the trunk circuit. If battery is connected to conductor 3! 4, relay 126 operates over a circuit from conductor 3I4, brush 4I1, conductor 9, inner upper front contact of relay 5I2, brush 523, conductor 531, inner right back contact of relay I21, left normal contacts and winding of relay 126 to ground at the middle left front'contact of relay 101. If battery is connected to conductor 3I6, relay 121 operates in a circuit from conductor 3I5, brush 4I6, conductor 420, next to inner upper front contact of relay 5I2, brush 522, conductor 529, inner right back contact of relay 126,

left normal contacts and winding of relay 121 to ground at the outer left front contact of relay 101. If battery is connected to conductor 3| 8 and ground to conductor 320, relay 802 operates in a circuit from battery on conductor 3I 8, brush 4I5, conductor 432, contact 530 of relay 5I2, brush 52I, conductor 53I, right back contact of relay 804, inner left front contacts of relay 80I, outer left back contact of relay 800, windings of polarized relays 802 and 803 in series, back contact of relay 805, left back contact of relay 804, conductor 538, brush 520, contact 532 of relay 5I2, conductor 433, brush M4, to ground on conductor 320, polarized relay 803 not receiving current in the proper direction to operate. Relay 802 in turn closes a circuit from battery, winding of relay 128, left back contact of relay 129, conductor 806, contact of relay 802, conductor 801 to ground on conductor I I 4. If battery is connected to conductor 320 and ground to conductor 3I8, current flows through the windings of polarized relays 802 and 83, in such a direction as to. operate relay 803 which in turn closes a circuit from battery through the winding of relay 129, left back contact of relay 128, conductor 808, contact of relay 803 to ground over conductors 801 and H4. Either relay 128 or 129 upon operating looks over its outer right front contact to ground on conductor 1I4. Either relay 126 or 121 upon operating locks in a circuit from ground at a left contact of relay 101 through its winding and outer left alternate contacts to battery through resistance 130.

Circuits for class relays I000 to I003, inclusive, are closed as follows: with relays 121 and 129 operated, class relay I000 is operated in a circuit from battery through its winding, conductor I004, inner right front contact of relay 129, right alternate contacts of relay 121 to ground; with relays 126 and 129 operated, class relay Il is operated in a circuit from battery through its winding, conductor I005, middle right front contact of relay 129, outer right front contact of relay 126, outer right normal contacts of relay 121 to ground; with relays 121 and 128 operated, class relay I002 is operated and a circuit through its winding, conductor I006, inner right front contact of relay 128 to ground at the outer right alternate contacts of relay 121; and with relays 126 and 128 operated, class relay I003 is operated in a circuit from battery through its winding, conductor I001, middle right front contact of relay 128, outer-right front contact of relay 126, to ground at the outer right normal contacts of relay 121.

In the case assumed, the trunk of Fig. 3 is of a fixed four digit class requiring immediate ringing from the sender only in case the call is being completed by an inward toll operator and requiring a short interval of 0.4 second between the last two impulse series which are to be transmitted therefrom to set the connector switch and consequently straps 309 to 3l2 are connected as shown: to connect conductor 3I4 to conductor 3| 3 and thence over the inner upper back contact ofrelay 32I, tips of jack 30I and plug I24, left normal contacts of key I I5, inner upper front contact of relay I03, conductor 205, upper front contact of relay 206, normal contacts and windings of relay 22I, inner lower alternate contacts of relay 2I0 to ground at the inner lower normal contacts of relay 2I3; to connect conductor 3N to conductor SI and thence over the inner lower back contact of relay 32I, rings of jack MI and plug I24, the inner lower front contact of relay 223, conductor 208, the lower front contact of relay 206 to 24-volt battery through the inner upper normal contacts of relay 2H] and the low resistance 2l8; to connect conductor 3l8 to conductor 3H, thence over the upper back contact of relay 32!, the upper back contact of relay 322 through one winding of the control relay (not shown) of the first selector 350 in which the trunk of Fig. 3 terminates; and to connect con ductor 320 to conductor 3| 9, thence over the lower back contact of relay 32I, the lower back contact of relay 322 tobattery through the other winding of the control relay of first selector 350. Thus as above described, sender relays I21, 129 and class relay I200 are operated.

With relay 12! operated the circuit previously traced from 24-volt battery at the key-set circuit to conductor 529 is now extended over the right back contact of relay I26, inner left front contact of relay 121, right back contact of relay 122 to the right back contact and right winding of relay Ill, thence as traced to ground on conductor l l 6 and the circuit previously traced from ground through the normal contacts and winding of relay 22! at the key set circuit to conductor 531, is now extended over the inner right front contact of relay l2'l, the inner left back contact of relay 122, left back contact of relay 'Hl, condenser E22, left winding of relay 1", thence as traced to ground. This latter circuit serves as a discharge path for condenser 12!] which now discharges through the left winding of relay ll'l. This discharge current now aiding the current flowing through the right winding of relay ill, relay li'! operates establishing a holding circuit for itself from 24-volt battery through low resistance 123, right alternate contacts and right winding of relay 'lll, outer left back contact of relay 122 to ground at its outer left contact and connecting ground over its outer left front contact to conductor E24 preparatory to operating the holding magnets 603 and 604 of the key-set connector switch 650 which magnets are allocated to the sender disclosed.

At its inner left back contact relay I ll disconnects condenser [26 and 48-volt battery through high resistance 12! from the circuit previously.

traced through the winding of relay 22! at the key-set circuit and at its inner left front contact connects 24-volt battery through low resistance 125 to this circuit causing the operation of relay 22%. Relay 22! upon operating looks over its upper alternate contacts to battery through resistance 2 l8 and establishes an operating circuit for relay 2l9 extending from battery, winding of relay 2l9, lower front contact of relay 22l, upper back contact of relay 222, inner lower alternate contacts of relay 213, inner lower normal contacts of relay 2l3 to ground. At its lower front contact, relay 2553 establishes acircuit from ground over the upper back contact of relay 223, conductor 224, to battery through the winding of horizontal magnet 685 of switch 656 which operates. Horizontal magnet B95 identifies the particular calling operators position in the keyset connector switch 656, magnet 635 to 6&5 similarly identifying nine other operators positions.

Magnet 285 upon operating rotates a horizontal bar of the switch into a position which is effective to cause the operation of contact sets in the uppermost horizontal row of contact sets and at its contact completes the operating circuit of the holding magnets 6G3 and 554 which may now be traced from battery, front contact of magnet 625,

normal contacts of magnet 604, windings of magnets 503 and BM in parallel, conductor 24 to ground at the outer left front contact of relay Hi. Magnet 6% upon operating connects looking battery to the windings of the magnets 323 and 604 so that they are now independent of the continued operation of magnet 625 and both magnets also rotate the vertical bars of the switch controlled thereby which in cooperation with the vertical bar operated by magnet 6-35 causes the operation of the contact sets 686 and 631 to their closed positions. These contact sets are held operated by the magnets 633 and 604 after the subsequent restoration of the horizontal bar through the release of magnet 6B5. Holding magnet- 663 upon operating also establishes an obvious circuit through the upper Winding of relay 669, which operates and looks over its lower Winding and front contact to ground on conductor 155. At its back contact, relay 60H opens the holding circuit of relay 6535, thus releasing relays 38! and 692 freeing the allotter circuit. The operation of the contact sets extends ten conductors from the outside passive contacts of the keyset 226 to the horizontal magnets to 909, inclusive, of the sender register switch 9H3 of Fig. 9 and a conductorfrom start key 243 to the winding of relay 5921' of Fig. 10, and'establishes a circuit from ground over the upper contact of contact set 601, conductor 225 to battery through the winding of relay 223. Relays Hi2! and 223 operate, relay 223 opening the operating circuit of magnet 625 which releases thus restoring the operated horizontal bar of switch 652 and opening the initial operating circuit of magnets 62% v and 624.

'Relay 223 upon operating looks over its inner lower front contact to ground at the lower front contact of relay 213, establishes a circuit from ground at the lower contact of relay 2 l9 over its upper front contact and the lower back contact of relay 222 to battery through lamp 226 which lights as a signal that the keys of the key-set 220 are now connected with the register of the selector sender and supplies operating ground from the lower contact of relay 2 l 9 over its lower front contact and conductor 232 to the outer active contacts of the keys of key-set 22B and to the active contact of start key 243.

Should the operator depress a key of the keyset 220 before the senderis attached and relay 2 ii has operated, relay 222 is operated in a circuit extending from battery, winding of relay 222, upper back contact of relay 2 l9, inner contact of the operated key-set key to ground at the inner lower front contact of relay 265. Relay 22 upon operating locks over its inner lower front contact and the left normal contacts of key 239, the inner lower alternate contacts of relay 2m and the inner lower normal contacts of relay 2 l3 until key 209 is reoperated and, at its lower front contact, establishes a flashing circuit for lamp 222 through interrupter 221. The flashing of lamp 226 indicates to the operator that she has prematurely depressed a key-set key. She will therefore proceed to reoperate key 269 thereby releasing relay 222 and await the steady lighting of lamp 225 as a signal that a sender has become connected to her key-set.

Keying the called Zine designation It will be assumed that the operator in order to establish a connection to line 399, the designation of which is the four digit number i379, depresses keys 228, 229, 239 and 23l inthe order named. Upon the depression of key 228 to register the thousands digit 1, ground from conductor 232 is connected over the outer contacts of key 228, conductor 233, lowermost contact of contact set 691, conductor 699, winding of horizontal magnet 99| to battery. Magnet 99| upon operating rotates the lowermost No. horizontal bar of the register switch 9|9 and closes a circuit from ground over its front contact, back contact of transfer relay 9| lower normal contacts and winding of vertical magnet 9|2 to battery. Magnet 9|2 operates, looks over its lower alternate contacts to ground on conductor H5, connects ground from conductor H5 over its upper front contact through the winding of transfer relay 9| resistance 921 to battery and rotates the first vertical bar of switch 9|9. Relay 9|! does not operate at this time since its winding is shunted by ground potential applied over the front contact of magnet 99! and the upper back contact of relay 9| to a point between resistance 921 and the winding of relay 9| With the lowermost horizontal bar and the first vertical bar of switch 9| 9 both operated, the contact set 928 is operated and held operated under the control of magnet 9|2 after magnet 99| releases to return the operated horizontal bar to normal when the operated key 228 is released. When magnet 99| releases, the shunting ground is removed from the winding of transfer relay 9| and it now operates.

When the operator depresses key 229 to register the hundreds digit 3, ground from conductor 232 is connected over the outer contacts of key 229, conductor 234, contact 699 of contact set 691, conductor 6|9, winding of horizontal magnet 993 to battery. Magnet 993 upon operating rotates the No. 3 horizontal bar of switch 9|9 and closes a circuit from ground over its front contact, upper front contact of transfer relay 9| upper back contact of transfer relay 9| 3, lower normal contacts and winding of vertical magnet 9M to battery. Magnet 9|4 operates, locks over its lower alternate contacts to ground on conductor H5, connects ground from conductor H5 over its upper front contact through the winding of transfer relay 9|3 and resistance 929 to battery and rotates the second vertical bar of switch 9|9. Relay 9|3 does not operate at this time since its winding is shunted by ground applied over the front contact of mag-' net 993, the upper front contact of relay 9| I and the upper back contact of relay 9|3 to a point between the resistance 929 and the winding of relay 9|3. With the No. 3 horizontal bar and the second vertical bar of switch 9|9 both operated,

the contact set 939 is operated and held operated under the control of magnet 9|4 after magnet 993 releases to return the operated horizontal bar to normal when the operated key 229 is released. When magnet 993 releases, the shunting ground is removed from the winding of transfer relay 9|3 and it now operates.

When the operator depresses key 239 to register the tens digit 7, ground from conductor 232 is connected over the right contacts of key 239, conductor 235, the next to the lower contacts of contact set 696, conductor 6, winding of horizontal magnet 991 to battery. Magnet 99! upon operating rotates the No. 1 horizontal bar of switch 9|9 and closes a circuit from. ground over its front contact, upper front contact of transfer relay 9| inner upper front contact of transfer relay 9|3, upper back contact of transfer relay 9|5, lower normal contacts and winding of vertical magnet 9|6 to battery. Magnet 9| 6 point between resistance 93| and the winding of relay 9| 5. With the No. 1 horizontal bar and the third vertical bar of switch 9| 9 both operated, the contact set 932 is operated and held operated under the control of magnet 9|6 after magnet 99'! releases to return the operated horizontal bar to normal when the operated key 239 is released. When magnet 99! releases the shunting ground is removed from the winding of transfer relay 9|5 and it now operates.

When the operator depresses key 23| to register the units digit 9, ground from conductor 232 is connected over the right contacts of key 23|, conductor 236, contacts 6|5 of contact set 696, conductor 6|2, winding of horizontal magnet 999 to battery. Magnet 999 upon operating rotates the No. 9 horizontal bar of switch 9|9 and closes a circuit from ground over its front contact, upper front contact of transfer relay 9| inner upper front contacts of transfer relays 9| 3 and 9|5, inner upper back contact of transfer relay 9|'|, lower normal contacts and winding of vertical magnet 9| 8 to battery. Magnet 9| 8 operates, locks over its lower normal contacts to ground on conductor H 5, connects ground from conductor H5 over its upper front contact through the winding of transfer relay 9|! and resistance 933 to battery and rotates the fourth vertical bar of switch 9|9. Relay 9|? does not operate at this time since its winding is shunted by ground potential applied over the front contact of magnet 999, upper front contacts of relays 9||, 9|3 and 9|5 and the upper back contact of relay 9| I to a point between the resistance 933 and the winding of relay 9H. With the No. 9 horizontal bar and the fourth vertical bar of switch 9|9 both operated, the contact set 934 is operated and held operated under the control of magnet 9|8 after magnet 999 releases the operated horizontal bar to normal, when the operated key 23| is released. When magnet 999 releases, the shunting ground is removed from the winding of transfer relay 9| 1 and it now operates.

Since it was assumed that class relay I999 was operated indicating a call of the four digit fixed class, when transfer relay 9| 1 operates, a circuit is established from ground on conductor 1 l5, outer left front contact of class relay I999, conductor I998, lower front contact of transfer relay 9|1, conductor Hi2, winding of relay 122 to battery. Relay 122 operates, releases relay H! and disconnects the armatures of relay H7 from conductors 529 and 53? and connects these conductors to the' right operating windings of relays l3| and 132. The release of relay 1|! opens the.

locking circuits of magnets 993 and 699 of keyset connector switch 659 thereby restoring this switch to normal.

A circuit is now established from 2 l-volt battery through the winding of polarized relay 231 at the key-set circuit, left normal contacts of key 239, upper alternate contacts of relay 2|9, lower front contact of relay 296 thence as traced to conductor 529', right back contact of' rel'ay I26, inner right front contact of relay I21, right front contact of relay I22, inner left back contact of relay I33, inner left back contact of relay I34, right winding of relay 'I3I, to 48-volt battery. A second circuit is established from 24-volt battery through the winding of polarized relay 238 at the key-set circuit, right normal contacts of key 239, upper front contact of relay 206, thence as traced to conductor 531, inner right front contact of relay I21, left front contact of relay I22, right back contact of relay I33, right back contact of relay I34, right winding of relay I32 to LS-volt battery. Polarized relays 231 and 238 both operate, but relays l3! and I32 being marginal do not. With relays 231 and 238 both operated, a circuit is established from ground over their front contacts to battery through the winding of relay 240 which relay operates and looks over its upper front contact, upon back contact of relay 222, to ground over the inner lower alternate contacts of relay 2 I and the inner lower normal contacts of relay 2I3 and at its upper front contact connects ground to the winding of polarized relay 231 for holding it operated and over the circuit previously traced through the right winding of marginal relay 73! in the sender.

Relay 'I3I now operates and locks'in a circuit from ground on conductor H5, contact and left winding of relay 'I3I,' winding of relay I33 to battery. Relay I33 operates, opening the circuit through the operating winding of relay BI and the winding of polarized relay 231, and the circuit through the operating winding of relay T32 and the winding of polarized relay 238. Polarized relay 239 now releases but relay 231 is held operated under the control of relay 240.

Relay 239 upon releasing establishes a shunt circuit around the winding of relay 2I0 which may be traced from ground, back contact of relay 238, lower front contact of relay 240, winding and inner upper front contact of relay 2I0 to ground at release key 2I4 or ground on conductor 2| I, whereupon relay 2i0 releases in turn releasing relays 206, 2I9, 22I, 231, 223 and 240. Relay 2i0 upon releasing also opens the circuit of key talking circuit between the tip and ring contacts of plug I00 and the tip and ring contacts of plug I24. The key set is now completely disconnected from the cord circuit and from the sender and may be used with another cord circuit of theoperators position to control the setting up of another connection.

Transmission of impulses to selector switches Returning to a consideration of the sender, it will be recalled that transfer relay 9| I operated when the first digit was registered on the register switch 9I0. A circuit was therefore established from battery through the winding of steering relay 935, lower back contact of transfer relay 9I3, lower front contact of transfer relay 9, conductor 943, upper normal contacts of relay I009 to ground on conductor "5. Relays 935 to 942, inclusive, are steering relays for the outpulsing circuit and shift the pulsing control from the register contacts of one vertical row of switch 9I0 to the next vertical row after the impulses for one digit are all sent out. Relay 935 upon operating locks over its inner lower front contact, conductor 943, upper normal contacts of relay I009, to ground on conductor H independent of transfer relay 9I3, establishes an operating circuit for relay IOI3, extending from battery, winding of relay IOI3, conductor 944, lower front contact of relay 935, inner lower front contact of relay 9! I to ground on conductor H5, prepares the operating circuit of the next steering relay 936, and connects ground potential over its middle upper front contact and conductor 945 to the lower control electrode of tube Initially neither tube IOI4 nor tube H5 is ionized and positive potential is applied from battery I026 to the upper or control electrode of tube IOI4 through resistances IOI6 and. IOII and to the upper or control electrode of tube IOI5 through resistances IOI6 and IOI8 and condensers IOI9, I020 and 'I02I are uncharged. The tube circuits areso arranged that when the impulser is to be started, tube IOI4 is ionized before tube IIlI5 can ionize, that is a pulse is sent out through the operation of impulsing relay I022 before an impulse is counted through the operation of impulse counting relay I023. When, as previously described ground is connected to the lower control electrode of tube IOI4, this tube ionizes across the gap between its control electrodes and current flows through the two resistances IOI6 and NIH. The resulting drop of potential across these resistances causes the condenser I020 to charge in a circuit from ground on conductor 945 across the ionized gap between the control electrodes through condenser I020, resistance I024 to the positive terminal of source I026. Also as a result of the breaking down of the gap between the control electrodes, the main gap between the lower electrode and the anode ionizes and current flows from grounded conductor 945 across the main gap through the winding of impulsing relay I022, resistance I025 to the positive terminal of battery I026.. The drop in potential across resistance I025 now causes condenser M9 to assume a charge.

As soon as relay IOI3 operates after an interval determined by its slow to operate characteristic, ground is connected over conductor I021 to the lower control electrode of tube IOI5 causing tube IOI5 to ionize across the gap between its control electrodes. The main gap between the lower control electrode and the anode is also ionized and current flows from ground on conductor I021 across the main gap through the winding of impulse counting relay I023, resistance I024 to the positive terminal of battery I026. The drop of potential across both resistances I024 and I025 is now the same. The result is that the same potential is now applied to both terminals of condenser IOI9 and this condenser discharges through resistances I024 and I925 and lowers the potential on the anode of tube IOI4 below the value required to sustain ionization across the main gap of this tube and also the lowering of the potential across resistances IOI6- and IOI3 upon the ionization of the control gap of tube IOI5 charges condenser I02I and-lowers the potential on the upper of control electrode of tube- IOI4 below the ionizing potential. Tube IOI0 therefore deionizes and releases relay I022. becomesionized the potential at the point of juncture between'condenser I020 and resistance I020-is lowered to a point such that both terminals of condenser I020 have the same potential. Condenser I020 therefore discharges in a path through resistances I024, IOI0 and Hill. As condenser i020 discharges the potential on the upper control electrode of tube IOI4 becomes less negative. After a time which is determined 'bythe constants of the condenser discharge circuit, the potential on the control electrode of tube I 0I0 -becomes sufiiciently less negative for the tube I 0I0-to again ionize. The above cycle of operationsis nowrepeated; when tube 10M again ionizes tube IOI5 deionizes; after a definite delay tube -IOI5 again ionizes and tube l0I4 deionizes. In this manner tubes I0! and IOI5 ionize and-deionize alternately under the control of condenser H9 at a rate which-is determined by'the g constants of the timing circuits controlled by' condensers I 020 and I 02 I.

When relay IOI3' operated, it established a circuit for relay -I'0I0- extending-from ground on conductor H5, back contact of relay 838,con- "cluctor I028, inner lower front contact of relay IOI3, lower normal contacts and winding of relay IOI0 through resistance I0 I2 to battery and in a branch of this circuit through the winding of relay I009 and resistance I 0 to battery. Relay "'IOI0 operates and locks over its lower alternate contacts to ground on conductor 1 I 5 and connects direct ground from conductor H5 to the winding of relay I009. Relay I009 does not operate, however, since its winding is shunted over its lower back contact so long as relay 838 remains unoperated; Relay IOI0 upon'operating establishes an operating circuit for. steering relay 938 which may be traced from battery, winding of relay 938, next to inner lower front contact of relay 935, conductor 946, upper front contact of relay IOI0 to ground on conductor H5. Relay 936 operates but is without function at this time.

The first operationof impulsing relay I022 resulting from the initial ionizationof tube IBM is without effect. When tube IOI5 ionizes for the first time, it deionizes. tube I0l4 releasing relay I022 and operates relay.I023. A circuit is thereupon established from ground at the upper front contact of relay IOI3, conductor I029, back contact of relay I35, right back contact of relay I36, conductor I31, inner left back contact of relay 800, conductor I030, contacts of impulse counting relay I023, conductor I03I, left back contact of relay 809, left back contact of relay 8I3, right back contact of relay.8I I winding of relay 8I2 to battery. Relay 8I2 operates and.

locks in a circuit through its winding and the Winding of relay 8I I inseries, inner left front contact of relay 8I2, right back contact of relay 8 I3, to ground on conductor H5, but the winding of relay 8II being shunted so long as impulse counting relay I023 remains operated, relay 8II does not operate. Relay .8I2 upon operating establishes a circuit for the pulse help relay 805 extending from battery through the winding of this relay, inner left front contact of relay 8I2, right back contact of relay 8I3 to ground on conductor H5 and at its right contact opens a shunt around the contacts of impulsing relay I022, thereby rendering relay I 022' effective to When themain gap of tube IOI5-- transmit'impulsesw The outpulsing circuit is now established fromthe-upper winding of the control relay of the first selector 350, thence as traced to conductor 53I, right back contact of relay 804, left front contacts of relay I, outer.

Tube IOI5 deionizes following the deionization of tube IOI4 and releases relay I023 which removes the shunt from the winding of relay 8I I. Relay 8 now operates. The operation of relays 8| l and 8I2 has thus been effective to absorb the first impulse produced by impulsing relay I 022. Tube IOI4 now reionizes operating relay I022 which is now effective to open the outpulsing circuit just traced, whereupon the first selector advances its brushes one step vertically in the well-known manner. Tube IOI5 reionizes follow- 7 ing the ionization of tube IOI4, reoperating relay I023 which now closes a circuit from ground as previously traced to conductor I030, contacts of relay I023, conductor I 03I left back contact of relay 809, left back' contact of the No.1 counting relay 8I3, front contactof relay 8H; back contact of the No. 2' counting relay 8| 5, conductor 835, inner upper front contact of steering relay 935, contact set 9280f switch'QIll, conductor 941, winding of the NO. I counting relay 8| 4 to battery. Relay 8| 4 operates and locks through its winding and the winding of the No. I counting relay 8I3 in series, front contact of relay 8I4, left back contact of relay 8I9 to ground on conductor II 5, but relay 8| 3 being shunted does not operate. When tube IOI5 reionizes, tube I 0I4 deionizes and releases relay I022 to reestablish the outpulsing circuit followed by the deionization of tube IOI5 and the release of relay I023. Relay I023 upon releasing opens the shunt around-the winding of relay 8i 3 and the latter relay now operates releasing relays M I, BIZ and 805. Upon the release of relay 8I2, the shunt around the contacts of impulsing relay I022 is closed rendering relay I022 ineffective to transmit further impulses over the outpulsing circuit and with relay 805: released the outpulsing circuit extends as traced to conductor 53I thence over the right back contact of relay 804, left front contacts of relay 80I, outer left back contact of relay 800,5.Windings of polarized relays 802 and 803, back contact of relay 805, left back contactof relay 804,.conductor. 538, thence .as

time delay interval during which the first selector hunts for an idle trunk in the. first level to which its brushes were advanced.

On thenext ionization of tube I 0| 5 and the operation of relay I023, a circuit is established from ground on conductor I030, contacts of relay I023, conductor. I031; left back contact of relay 809,-left front contact of the No. I' counting relay 8I3, winding of relay 8I0 to battery. Relay 8i0 operates-and locks in series with relay 809,'front contact of relay 8I0, conductor I036, inner upper front contact of relay IOI3, conductor I032, innerright normal contacts of relay 809 to ground'on conductor 'II5,.but relay 809 being shunted does not operate. On the next deionization of tube IOI'5 and the release of relay I023,-:re1a -809operates and establishes a new holding circuitforitself and relay 8I0 as traced 

